This invention relates to solid propellants, and in particular, to burn rate catalysts for solid propellants.
It is a common practice to use solid or plastic propellant mixtures in the combustion chambers of rocket motors. Such propellants are burned to produce gaseous combustion products which are exhausted through a nozzle at high velocity, thereby producing a thrust. The burning rate of solid propellants affects the amount of thrust obtained per unit of given cross section, the thrust developed being dependent upon the volume of gases liberated per unit time.
A solid rocket propellant comprising a major amount of ammonium perchlorate, a minor amount of aluminum powder and a minor amount of a hydroxy-terminated polybutadiene binder, for example, will burn with relative freedom from smoke, but may not develop a desired level of thrust. Several substances have been added to solid propellants to accelerate the burning rate to a desired level. Well known examples of burn rate modifiers or catalysts are ferric oxide, ferric fluoride, copper chromite, ferrocene and certain derivatives thereof, and vanadium pentoxide. Each of these catalysts has one or more drawbacks. The iron salts may interfere with propellant mixing and cure; copper chromite may catalyze oxidation of the binder at room temperature. The ferrocenes tend to migrate out of the propellant while in storage. Vanadium pentoxide presents health hazards to workers during propellant formulation, casting and curing. Certain burn rate catalysts which, while increasing the burning rate somewhat, incidentally make the propellant composition sensitive to shock, thereby creating an explosion hazard.
U.S. Pat. No. 3,740,702, issued Apr. 3, 1956, to Harry W. Mace, discloses an ammonium perchlorate-asphalt type of propellant catalyzed with chromium sesquioxide (Cr.sub.2 O.sub.3), ferrosoferric oxide, or a mixture of Cr.sub.2 O.sub.3 with an oxide taken from the group of metal oxides consisting of ZnO, Fe.sub.2 O.sub.4, TiO.sub.2, SnO.sub.2, Al.sub.2 O.sub.3 and CuO. There is no disclosure of the use of Cr.sub.2 O.sub.3 in a propellant composition comprising ammonium perchlorate, aluminum powder and a hydroxy-terminated polybutadiene.
I have discovered that Guignet's green pigment is superior to chromium sesquioxide as a burn rate catalyst in a propellant composition comprising ammonium perchlorate, aluminum powder and hydroxy-terminated polybutadiene. I have further discovered that oxidized Guignet's green pigment is an effective low-pressure burn rate catalyst.
Accordingly, it is an object of the present invention to provide an improved solid rocket propellant composition.
Other objects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following description of the invention.